The two primary objectives outlined in this proposal are concerned (1) with the cellular factors involved in the development by a plant tumor cell of a capacity for autonomous growth, and (2) with an attempt to program tumor cells, under defined experimental conditions, into a form of terminal differentiation that results in the loss of their neoplastic properties. Interest in the first objective has centered on the chemical nature and mode of action of a new class of cell division-promoting factors, the cytokinesins. These substances have been found to be potent inhibitors of cAMP (3',5') phosphodiesterases, and an attempt will be made to determine whether their cell division-promoting activity can be explained by virtue of the fact that they act as regulators of cAMP (3',5'). A model system has been worked out and the essential factors characterized for inducing cells into a form of terminal differentiation that results in death.